Evaluation of in vitro bioactivity and tribological behaviour of sustainable bio-waste-reinforced biodegradable ZK61 hybrid composites for orthopaedic applications

Bioactivity and tribological behaviour of bone fixation materials are critical determinants of their in vivo performance. Mg-based composites have received considerable interest as biodegradable implant materials owing to their mechanical compatibility with natural bone, which mitigates stress-shielding effects, and their excellent biodegradability, which obviates the need for follow-up surgery in orthopaedic applications. However, the performance of magnesium under service conditions is constrained by its susceptibility to tribological damage. To overcome this limitation, ZK61 Mg-matrix composites are fabricated with hybrid reinforcement – hydroxyapatite (10 wt.%) and eggshell (2.5 wt.%) – using friction stir processing. In this present work, ZK61-10HA-2.5ES Mg-matrix composites are marked in terms of microhardness, wettability, in vitro bioactivity and wear performance. Dry sliding wear performance was assessed using pin-on-disc tests at a load of ∼45 N for 600 seconds. The ZK61-10HA-2.5ES composite exhibited a significantly lower coefficient of friction and wear rate than the base ZK61 alloy, showing superior wear resistance. The scanning electron microscopic micrographs indicated that abrasive wear through micro-ploughing was the predominant wear mechanism, with reduced wear severity in the composite compared with the base alloy. The outcomes of this investigation provide a valuable foundation for the development of next-generation biodegradable composites based on ZK61-10HA-2.5ES for orthopaedic applications.